1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for measuring channel quality by using a ranging signal in a broadband wireless communication system.
2. Description of the Related Art
In the next generation communication system, also known as the 4th Generation (4G) communication system, research is in progress to provide a Quality of Service (QoS) with a data transfer speed of about 100 Mbps. More particularly, the 4G communication system is currently being developed to ensure mobility and QoS in a Broadband Wireless Access (BWA) communication system, such as a Wireless Local Area Network (WLAN) system and a Wireless Metropolitan Area Network (WMAN) system. A representative example of the 4G communication system is described in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard.
In a broadband wireless communication system, such as in the system based on the IEEE 802.16 standard, a Mobile Station (MS) transmits a pre-agreed ranging signal to a Base Station (BS) when an initial access process is performed between the MS and the BS. The BS then estimates a time offset of the MS by using the received ranging signal, and reports time offset information to the MS. Accordingly, the MS transmits a signal by considering the time offset. Thus, the time offset is compensated for. Further, the BS measures channel quality by using the ranging signal, and utilizes the measured channel quality in power control or the like to be performed later. For example, the channel quality may be a Carrier to Interference and Noise Ratio (CINR).
As described above, the BS measures the channel quality and the time offset by using the ranging signal received from the MS. However, in the process of measuring the channel quality, the BS measures the channel quality by using the ranging signal including the time offset. The channel quality measured using the ranging signal is utilized when communication is performed after the time offset is compensated for. Therefore, the channel quality measured using the ranging signal is lower than actual channel quality due to the time offset. That is, distorted channel quality information is used in a process for controlling communication, which leads to a problem of system performance deterioration.
Therefore, a need exists for a system and method for measuring channel quality in a broadband wireless communication system that avoids system performance deterioration.